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C4, sequence, flowchart, use case, ER or dictionary — .alab, arch-lab JSON, or Mermaid, auto-detected and rendered live. Nothing leaves your browser. Syntax reference

How .alab, JSON and Mermaid relate

.alab is the format to write: it is what the syntax reference documents, what share links carry, and what reads cleanly in a code review. .archlab.json is the same C4 model on disk — the interchange form any other tool can read without implementing a grammar; the two are lossless twins in both directions (proved on every build), so you never have to write the JSON by hand. Mermaid is read and written too, lossily — the format toggle above the pane converts in place and states what each direction drops. Nothing you type is uploaded or stored.

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archlab 1.0 dict
title "order.placed event"
description "The envelope and payload every downstream consumer subscribes to — a contract with no table behind it."

@dict
  section "Envelope" [Kafka]
    desc "Present on every event on the topic, whatever the payload"
    field event_id uuid required unique
      desc "Deduplication key. A consumer that has seen this id has already processed the event."
      values "RFC 4122"
    field occurred_at timestamptz required
      desc "When the thing happened, not when the message was produced. Producers retry; this does not change."
    field version integer required
      desc "Schema version of the payload below. A consumer must ignore an envelope whose version it does not know."
      example "3"
  section "Payload"
    desc "Version 3. Fields are added, never removed or repurposed."
    field order_id uuid required
      desc "The order this event is about."
      source "orders.order.id"
    field customer_email string required pii
      desc "Denormalised onto the event so consumers need no lookup. Personal data — it leaves the boundary with the event."
      source "accounts.customer.email"
    field total_minor integer required
      desc "The order total in MINOR units, to avoid a float. Divide by 100 for a display value."
      example "128450"
    field currency string required
      values "ISO 4217"
      example "THB"
    field coupon_code string deprecated
      desc "Never populated since v2. Read the discounts array instead; this stays for consumers not yet migrated."

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